In recent years, in an image forming apparatus (for example, an MFP), a sheet finishing apparatus is provided to be adjacent to the latter stage of the MFP in order to finish a sheet after image formation. The sheet finishing apparatus is called a finisher, and forms a punch hole in a sheet fed from the MFP or staples the sheet. Alternatively, the finisher folds a sheet bundle in half and ejects it.
In order to form the punch hole in the sheet, the finisher includes a puncher having plural punching blades. The punching blade moves up and down by rotation of a punch motor, and the punching blade moves down toward the sheet surface, and forms the punch hole in the sheet. In some puncher, first punching is performed by half rotation of a punch motor in one direction, and next punching is performed by half rotation of the punch motor in the reverse direction.
After forming the punch hole in the sheet, the puncher stops the punching blade at an upper position and stands by. When the punching blade is separated from the paper surface, is moved up and is located at a standby position, the standby position is the home position.
In a related art puncher, after the punch hole is formed in the sheet, the punching blade is stopped at the home position. However, since a punching time is short, the punch motor is required to be rotated at high speed. However, in the case the punch motor is driven at high speed, when the punching blade is attempted to be stopped at the home position, even if the punch motor is braked, it is difficult to stop the punching blade at the home position. Accordingly, when the punch motor is stopped, the motor is rotated in the reverse rotation direction to be braked and is stopped.
Besides, since a load caused when the punching blade is operated varies due to an assembly error of parts constituting the puncher and a difference in environment such as low temperature and low humidity, it is difficult to accurately stop the punch motor. For example, when the reverse rotation braking is applied to the punch motor to stop it, when the load is low, the punch motor may exceed the expected position and stop at a position where the motor overruns in the opposite direction.
JP-A-2007-191245 discloses a sheet punching apparatus in which a load of a puncher is measured, and the drive amount of a punching blade is corrected based on the measurement result.
JP-A-2004-345834 and JP-A-2005-75550 disclose a sheet punching apparatus in which a slide link is moved by a DC motor, and a punch blade is moved up and down by sliding of the slide link. Besides, a stop control of the DC motor is described.
Besides, JP-A-2007-45605 discloses a sheet punching apparatus in which reverse rotation braking is applied and a punch blade is controlled to a home position.
However, in a puncher in which a punch motor is rotated in a forward direction to form a punch hole, and the punch motor is rotated in a reverse direction to form a punch hole, since a load in the forward driving and a load in the reverse driving are different, there is a defect that an error occurs when the punching blade is stopped at the home position. When the punching blade is not at the home position, there occurs a defect that when a punch hole is formed in a next sheet, a position shift occurs, or punching is not well performed.